Injury-Induced Senescence Enables In Vivo Reprogramming in Skeletal Muscle

In vivo reprogramming is a promising approach for tissue regeneration in response to injury. Several examples of in vivo reprogramming have been reported in a variety of lineages, but some including skeletal muscle have so far proven refractory. Here, we show that acute and chronic injury enables transcription-factor-mediated reprogramming in skeletal muscle. Lineage tracing indicates that this response frequently originates from Pax7+ muscle stem cells. Injury is associated with accumulation of senescent cells, and advanced aging or local irradiation further enhanced in vivo reprogramming, while selective elimination of senescent cells reduced reprogramming efficiency. The effect of senescence appears to be, at least in part, due to the release of interleukin 6 (IL-6), suggesting a potential link with the senescence-associated secretory phenotype. Collectively, our findings highlight a beneficial paracrine effect of injury-induced senescence on cellular plasticity, which will be important for devising strategies for reprogramming-based tissue repair.

Abnormal urethra formation in mouse models of split-hand/split-foot malformation type 1 and type 4

Urogenital birth defects are one of the common phenotypes observed in hereditary human disorders. In particular, limb malformations are often associated with urogenital developmental abnormalities, as the case for Hand-foot-genital syndrome displaying similar hypoplasia/agenesis of limbs and external genitalia. Split-hand/split-foot malformation (SHFM) is a syndromic limb disorder affecting the central rays of the autopod with median clefts of the hands and feet, missing central fingers and often fusion of the remaining ones. SHFM type 1 (SHFM1) is linked to genomic deletions or rearrangements, which includes the distal-less-related homeogenes DLX5 and DLX6 as well as DSS1. SHFM type 4 (SHFM4) is associated with mutations in p63, which encodes a p53-related transcription factor. To understand that SHFM is associated with urogenital birth defects, we performed gene expression analysis and gene knockout mouse model analyses. We show here that Dlx5, Dlx6, p63 and Bmp7, one of the p63 downstream candidate genes, are all expressed in the developing urethral plate (UP) and that targeted inactivation of these genes in the mouse results in UP defects leading to abnormal urethra formation. These results suggested that different set of transcription factors and growth factor genes play similar developmental functions during embryonic urethra formation. Human SHFM syndromes display multiple phenotypes with variations in addition to split hand foot limb phenotype. These results suggest that different genes associated with human SHFM could also be involved in the aetiogenesis of hypospadias pointing toward a common molecular origin of these congenital malformations.

Transfection of multiple pulmonary cell types following intravenous injection of PEI-DNA in normal and CFTR mutant mice

BACKGROUND

The polycationic vector polyethylenimine (PEI) has been shown to be a powerful agent for transfecting the mouse lung after injection of plasmid-based polyplexes through the tail vein. These findings raise therapeutic prospects for a number of lung conditions. For such potentials to be realised, the precise identity of the transfected cells remains to be determined; however, so far, no ultrastructural analysis has been performed on PEI-transfected lungs. The definition of which pulmonary cells are transfected is particularly critical for certain pulmonary diseases which might require transfection of defined cell types such as epithelial cells for cystic fibrosis (CF).

METHODS

Here, we use a combination of light and electron microscopy to determine which cells are transfected in the lung after PEI-mediated gene delivery through the intravenous route. Furthermore, we extend the same experimental setting to a mouse model of CF to provide proof of principle that this approach can be used in genetic models of the disease.

RESULTS

We show that within 18-20 h after injection through the tail vein, DNA/PEI complexes have already crossed the capillary barrier resulting in high levels of expression of reporter genes in the lungs. Transgene expression is observed in endothelial cells, in type I and type II pneumocytes, and in septal cells. Coexpression of the transgene and of the endogenous CF transmembrane conductance regulator (CFTR) gene is observed in some of the targeted epithelial cells. Levels and sites of expression are similar in normal and in CFTR-mutant mice.

CONCLUSIONS

The results demonstrate that PEI-mediated gene delivery leads to transfection of epithelial cells beyond the endothelial barrier and show that this method can be used for lung gene delivery in CF fragile mutant mice.